Models for the Asymmetric Enol borinate reduction of a ketone
A key stage in the reaction in the rearrangement of an enol borinate
is the C-C bond formation to an
aldehyde, mediated by the chiral auxilliary
X=di-isopinocampheyl (see I. Paterson et al, Tetrahedron,
1990, 46, p 4663; 1991, 47, pp.3471-3484)
A 3D model for the basic framework (i.e. replacing all substituents with H)
of the transition state must be constructed. Since this involves bond formation and cleavage, a QM
(Quantum Mechanics) based model must be used, in this case the AM1 semi-empirical method.
These calculations reveal that both chair and boat forms of the transition state are possible.
The boat transition state is shown below: